Abstract
We describe a case of a 20-year-old healthy man developing chest pain and classical symptoms of vaccine reactogenicity 12 h after receiving the first dose of mRNA-1273 (Moderna). Cardiac troponin T was increased, and subepicardial inflammation and focal contractile dysfunction were detected by cardiac magnetic resonance imaging and echocardiography. We confirmed the diagnosis of acute myocarditis by endomyocardial biopsy demonstrating significant infiltration of monocytes and T lymphocytes. Although we detected IgG against nucleocapsid protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) indicating prior infection, the patient repeatedly tested negative for SARS-CoV-2 and had been asymptomatic for several months. Furthermore, viral genome analysis of endomyocardial biopsy samples was negative for SARS-CoV-2 and other potential cardiotropic viruses. These findings and the strong temporal relation between the vaccination and the symptom onset imply a potential side effect of mRNA-1273.